Field of the Invention
The present invention relates to an image reading apparatus including an opening-closing unit disposed on an apparatus main body in an openable/closable state and a size detection unit for detecting a sheet size, and an image forming apparatus.
Description of the Related Art
An image forming apparatus such as a copying machine that includes an image reading apparatus mounted on the upper side of an image forming unit has been known. The image reading apparatus automatically reads an image regarded as a reading target formed on a sheet (hereinafter, referred to as “document”). The image reading apparatus includes a reading unit and an automatic document feeding device. The automatic document feeding device is disposed in an openable/closable state relative to a transparent glass (hereinafter, referred to as “document positioning glass plate”) provided on an upper face of a main body of the reading unit. An image reading unit for reading an image is disposed under the document positioning glass plate.
An image on a document is read through any of the two reading methods such as a feeding-reading method and a fixed-reading method. In the feeding-reading method, in a state where the automatic document feeding device is closed, the automatic document feeding device sequentially and individually conveys documents to the document positioning glass plate where the image reading unit is provided, so that the image reading unit automatically reads the images on the documents one-by-one. In the fixed-reading method, a user opens the automatic document feeding device to uncover the document positioning glass plate, and places a document on the document positioning glass plate. Thereafter, the user closes the automatic document feeding device so that an image on the document is read by the image reading unit.
In order to convey a document automatically, the automatic document feeding device includes a large number of built-in components such as various rollers and motors. Therefore, the automatic document feeding device has a weight of several kilograms to tens of kilograms, and thus it is not easy for a user to open or close the automatic document feeding device as it is. Therefore, the automatic document feeding device is normally provided with an opening-closing unit supporting unit having a hinge (hereinafter, referred to as “hinge unit”).
The hinge unit has a built-in spring in order to urge the automatic document feeding device in an opening direction that is a direction in which a weight of the automatic document feeding device (hereinafter, referred to as “own weight”) is cancelled. Therefore, the spring and own weight thereof are balanced with each other, so that a user can open and lift up the automatic document feeding device with little force and softly close the automatic document feeding device. The above configuration enables a user to easily place or remove a document on/from the document positioning glass plate.
In order to enable a user to easily place or remove a document on/from the document positioning glass plate, Japanese Patent Application Laid-Open No. 3-184059 discusses a configuration for favorably setting the balance between a spring and own weight. Further, in order to read a document placed on a document positioning glass plate, U.S. Pat. No. 8,861,047 discusses a configuration for automatically detecting a size of the document placed on the document positioning glass plate. In the above-described technique, an image reading unit reads an image of the document according to a detected document size. Then, information about the detected document size is reset when the automatic document feeding device is opened up to a predetermined position.
When a document placed on the document positioning glass plate is to be replaced, an angle at which the automatic document feeding device is opened may vary depending on the users. In a case where the automatic document feeding device is not opened up to a position where the size information is reset when a user replaces a document, the size information set for a previous document-reading operation will not be reset. Therefore, a problem arises that the document-reading operation is executed based on the size information set for the previous document-reading operation even if the user places a document that has a size different from the size set for the previous document-reading operation. Further, in order to solve the above problem, there has been provided a configuration in which the size information is reset when the automatic document feeding device is opened just a little. However, with this configuration, there is a risk that the size information may be reset when a user slightly touches the automatic document feeding device.